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Abstract
The relationship between the dietary level of vitamin E (VE) and the immune response
of broilers was studied in three experiments. Immunity was assessed as antibody production
to infectious bronchitis virus (IBV), SRBC, and Brucella abortus (BA) antigens, mitogenic
response to phytohemagglutinin A (PHA) and concanavalin A (Con A), cutaneous basophil
hypersensitivity (CBH) to PHA, and lipopolysaccharide induction of acute-phase proteins
(APP) and heterophilia. A range of VE (0, 10, 17.5, 25, 37.5, 50, 100, and 200 IU/kg)
levels were supplemented to a basal diet (corn-soy) containing 10.2 IU of VE/kg. We
found a dose-dependent increase in antibody production in response to attenuated IBV
between 0 and 25 IU/kg of supplemented VE and no further increase at higher levels.
Antibody levels to SRBC were higher in birds supplemented with 50 IU of VE/kg compared
to those supplemented with 0 or 200 IU/kg of VE. Antibody production in response to
BA antigens was not influenced by VE. Mitogenic responses were suppressed by supplemented
VE in Experiment 1 for PHA (25 IU/kg diet) and Con A (25 and 50 IU/kg diets). CBH
and APP levels were not affected by VE. Heterophilia was lowest at 50 IU/kg 6 h after
lipopolysaccharide injection (Experiment 1). Our study showed that moderate (25 to
50 IU/kg) levels of VE supplementation were most immunomodulatory and that high levels
were less effective.